Justification:
The Water Onion has a very restricted range in southern Thailand, with an extent of occurrence of about 641 km² and an area of occupancy of about 48 km². The population is severely fragmented by habitat loss (only 3-5% of the original habitat remains) and there has been rapid population declines in some areas as a result (70% decline in the Nakha River during the period 2003-2008), and there has been local extinction in some streams within its range. The threats to the habitats and the species (exploitation) are all ongoing, hence there is continuing decline in a number of parameters. The species is therefore listed as Endangered and it could well become Critically Endangered in the near future if these trends continue.

IUCN staff in the region are trying to raise awareness about this species and have also been promoting habitat restoration and reintroduction projects in an effort to conserve this species.

This geophytic plant grows in clear running fresh water, usually in wide and open streams and rivers a few centimetres to two meters in depth depending on the seasonal water level. The soil is usually a sandy loam or mixed gravel. Some streams are shaded, however, in all their sites Crinum receive sunlight at least temporarily (http://www.amaryllidaceae.org). It prefers water temperatures of 22-30°C.

Mature bulbs reach 7 cm in diameter and about 15 cm high. The elongated (up to two metres long) float in the direction of the current, or in stiller water are piled in loops. Flowering occurs mainly during the monsoon season (August-October). The inflorescence comprises five to eight flowers. The plant also reproduces vegetatively through the production of bulblets.

The data on the phenology of water onion and water depth in Nakha river, maintained by Mrs. Oy Onkhow (co-leader of a local community based organization – ‘Pleun Prai Sri Naka’ - involved in conservation work in Ranong Province, highlights the following:

January (average water depth of 3-4 m): germination from seeds and leaf production from bulbs starts

February - July (average water depth starts at 1-2 m in March and increases to 5-6 m by July): leaf growth

August (average water depth 6-8 m): flowering is initiated

September (average water depth 8-9 m): peak flowering

October (average water depth 6-9 m): seed formation

November to December (average water depth drops from 6 m down to 4 m): seed is dispersed and laves die back

Preliminary observations on the mid areas of the Nakha River, by a team of IUCN scientists on the 3rd of June 2008 revealed the following: The speed of water flow in mid areas of Nakha River ranged from 0.25-3 m/s. The main population is restricted to a 600 m stretch (width – 30 m; depth 1-2.5 m), which has a muddy substrate. The growth was very dense towards the edge of the river. The water flow in this stretch was below 0.3 m/s. The area received ample sunlight. The length of the leaves ranged from 1-3 m, with each bulb having 20-40 leaves. Several fish were observed in this stretch, beneath the thick growth of this plant, which provided an ideal refuge to them. A thin layer of sediment was clearly visible on the leaf surface. Clumps of washed out Water Onion were observed on either side of the river bank, these had been removed by the fast flow of the water.

The Water Onion is a very important aquatic plant that functions as a keystone species in its aquatic habitats. It provides important habitat for native freshwater fish species such as the Soro Brook Carp (Tor soro), which use it as a habitat to lay eggs. Other aquatic species such as water snails and frogs also use it as breeding habitat. Other native fish eat the young leaves of Water Onion.

The species is popular with aquarists because it is easy to maintain, highly tolerant of temperature and light variations. The bulb is also used to produce a cream for softening the skin.

Investigations carried out by IUCN revealed that a buyer in Kuraburi used to purchase about 10,000 bulbs/day from local communities about 10 years ago. However, this amount has declined sharply over the past four years. At present (2008), he purchases at the rate of 1 Baht per bulb, and sells it to an exporting company in Bangkok at 5 Baht/bulb. The export company sells each bulb for 2-5 US$, in foreign destinations.

A major threat to the habitat of this species is the dredging of rivers and streams for removal of sediment and rock for construction and land reclamation purposes (this has also increased the speed of water flow in habitats of the Water Onion, where entire subpopulations have been dislodged). Also threatened by diversion of the rivers and streams for agricultural purposes. There is also extensive changes in the ecology of the streams and rivers due to land use changes in the adjoining areas (e.g., clearing of forest for agriculture) and resultant land-based erosion and river bank erosion (the substrate of the Nakha and Kuraburi rivers has changed drastically over the past 10 years, due to erosion. The muddy substrate that facilitates the growth of Water Onion has been replaced by pebbles, rock and gravel, in large areas of these rivers. Collection of bulbs from the wild for sale to the international trade for home fish ponds and aquaria is also a threat which needs closer monitoring.

The Office of National Environmental Policy and Planning in Thailand (ONEPP) has declared this species as nationally endangered (http://www.onep.go.th/). Local conservation groups in the Ranong province have also initiated the conservation of this species in its wild habitats (Youth group and Plern Prai Sri Na Ca Conservation Group established by Klong Na Ca Wildlife Sanctuary). The youth group is involved in awareness campaigns, ex situ propagation of Water Onion in nurseries, rescue of dislodged Water Onion deposited on river banks and subsequent re-planting in the wild. The Pleun Prai Sri Na Kha Conservation Group, together with the local authority organizes tourist visits (in dinghy paddle boats) along Na Kha river to observe Crinum thaianum during its flowering period (October-December) every year. About 600 Thai tourists visited the area in 2007. A fee of 450 Thai Baht (ca. 15 US$) is charged to each visitor.